Polar bears were once thought to be aimless wanderers, continually on the move across the sea ice. Scientists now believe that polar bears, like other members of the bear family, have distinct territories, or home ranges.

A polar bear's home range can be enormous, far greater than that of any other species of bear. A single polar bear may rove across an area twice as big as the country of Iceland.

One Alaskan polar bear was found to have a home range 45 times the size of Tennessee's Great Smoky Mountains National Park, which supports some 400 black bears.

Scientists note that the size of a bear's range is determined by the amount of available food. Polar bears living in areas with an abundance of ice and seals have smaller home ranges.

A polar bear's home range often overlaps those of other polar bears. This is particularly true in food-rich areas.

An area where many home ranges overlap is called a subpopulation. Scientists have identified 18 subpopulations of polar bears in the circumpolar region. Polar bears learn to respond to seasonal changes in the distribution of seals. Cubs develop a knowledge of these patterns during the two or three years they spend with their mother.

Young polar bears may travel more than 1,000 kilometers (600 miles) to set up a home range apart from their mother's.

While scientists believe that most polar bears limit their travels to a home range of a few hundred miles, one satellite-tracked female surprised researchers by setting off on a trek of some 3,000 miles. The power-walking bear began her journey at Alaska's Prudhoe Bay. From there she traveled across the top of the world to Greenland, where she spent the winter before moving on to Canada's Ellesmere Island and back to Greenland again.

Sources: Bears, Bears, Bears by Wayne Lynch (Firefly Books, Willowdale, Ontario, 1995); Polar Bears by Ian Stirling (University of Michigan Press, 1988); Anchorage Daily News (February 1996).